【作者】 胡广洪；

【导师】 崔振山；

【作者基本信息】 上海交通大学 ， 材料加工工程， 2009， 博士

【摘要】 随着近年来能源的紧缺,导致塑料原料价格不断上升,如何在保证产品性能的前提下来节约塑料原料,是目前研究的一个热点。微细发泡注塑成型就是在这个背景下所开发和研究的一项新技术,该技术通过在塑料熔体中加入超临界的CO2或者N2,使得在注塑制品内部形成致密的微孔,大小为5～100μm微孔的存在能够大大节约塑料原料,同时使得塑料制品具有较好的机械性能。目前这项技术已被广泛地应用于家用电器、航空航天、汽车等领域。研究表明微孔的尺寸太大,将会造成制品的质量问题,所以如何控制微孔形态以保证注塑产品的质量是该领域的研究方向之一。本文主要从成型工艺角度研究了工艺参数对微孔形态以及对最终产品质量的影响。本文在经典成核理论的基础上,考虑了超临界气体对聚合物熔体*自由能的影响,建立了聚合物熔体和超临界气体二元体系模型,根据单位摩尔体系中质量守恒,以及热力学化学势的计算模型,建立了聚合物熔体的自由能改变数学模型;同样考虑了聚合物和超临界气体两相表面能与纯聚合物表面能的差别,利用混合溶体*中的气体重量分数,建立了混合物的表面能计算模型。通过这两者对经典成核理论进行修正,提出了新的微细发泡注塑成型成核理论模型,将该模型应用于发泡体系中,得到了成核速率与饱和压力和溶体温度的关系,以及饱和压力与溶体温度对成核密度的影响。模拟结果与实验数据的比较,证明了基于新模型预测的成核过程与Colton和Kumar的实验结果有着较好的吻合,从理论上解决了Colton和Kumar的实验结果与经典成核理论不符的问题,表明了新模型比经典成核理论模型更能准确地反映整个成核过程。在总结前人利用经典微孔长大理论研究微孔形态与实际结果差别较大的基础上,结合数值模拟技术,将新成核模型作为长大模型的基础,对经典微孔长大模型进行修正;同时从扩散率、熔体黏度、表面张力以及聚合物和气体的性质等方面入手,建立了单一相溶体的物性模型,以此建立单一相溶体的物性参数数据库。基于这两项研究,提出了新的微孔长大模型,并以平板零件为例,研究了熔体温度、预填充量、注塑时间、冷却时间、超临界气体含量等工艺参数对微孔尺寸的影响趋势。基于本文所提出的微孔成核和长大理论,采用数值模拟和田口实验技术相结合的方法,通过对实验结果进行信噪比分析和方差分析,得到了相关工艺参数对微孔尺寸的影响比重,提出了避免微细发泡注塑成型零件缺陷的工艺调整方案。在此基础上,利用多元回归分析方法,在充分考虑工艺参数之间相互作用的基础上,建立了主要工艺参数对微孔尺寸影响的关系模型,并将其作为优化的目标函数,采用模拟退火优化方法,建立了数值模拟和优化方法的动态联系,对成型工艺参数进行优化,并将优化结果应用到平板模型中,得到了较理想的结果,确保了微细发泡注塑成型工艺参数设置的准确性和科学性。同时本文建立了基于数值模拟技术的工艺参数设计系统模型。将本文所提出的微孔成核和长大理论、数值模拟技术、田口实验技术、多元回归技术和优化技术有机地融合到该设计系统中,并在其基础上,利用VB编程,建立了一套完整的微细发泡注塑成型计算机工艺参数设计软件系统。该系统的建立使本文所提出的理论、工艺优化设计方案等被生产实际所使用成为可能。最后将微细发泡注塑成型工艺设计系统应用到复杂零件的实际生产中,利用本文研究的工艺设计方案和软件系统对实际复杂零件进行工艺参数优化设计,将所得的工艺参数应用到实际生产中,使产品的变形量从1.8mm减低到0.3mm以内,从而提高了产品的质量和满足了产品的设计要求。这说明了本文所论述的理论及方法是正确有效的,且对实际生产具有一定的指导作用。更多还原

【Abstract】 In recent years, the polymer resin price is rising due to the petroleum shortage. How to save plastics on the premise to ensure the plastics part quality is one of the research hotspots. Microcellular foam injection moulding process is developed in this background. There are large dense microcells in the injection plastics part because of the supercritical CO2 or N2 mixed into the plastics melt. It can save a lot of resin due to the microcells, which is about 5~100μm , in the part. At the same time, the parts also have good mechanical properties. So the technology is widely used in the homework appliance, aerospace and auto industy etc. But recent study shows that big cell size causes the injection part quality problems. Thus one of research directions in this domain is how to control the cell size to ensure the part quality. In this study, the effect of process parameters on the cell size and final part quality is deeply reserached.On the base of classical nucleation theory and effect of the supercritical gas on the free energy, the duality system model of polymer melt and supercritical gas is built. Thus refer to the constant of mass quantity in unit mole system and the calculation model of thermodynamic chemical potential, the free energy change mathematic model is founded. At the same time, considering the surface energy difference between the mixer of polymer melt and supercritical gas with only polymer melt, the mixer free energy calulation model is setup through the weight fraction of gas in the mixer. The free energy and surface energy of mixer is used to edit the classic nucleation theory. And the new nucleation model is built.The new nucleation theory is applied into a foam system. The relationship between nucleation velocity and density with the saturation pressure and melt temperature is obtained. At last the simulation result is compared with experiment results. The results by the new nucleation theory are consistent with experiment results by Mr. Colton and Vipin kumar well. So it shows that the new nucleation model is more accurate to present the whole nucleation process than the classical one.Considering the former work that large difference between the academic results with experiment, the classical cell growth model is edited from below two sides. One is the new nucleation theory is considered as the base of cell growth model. The other is that the material properties model of polymer-gas mixer is built by the improvement of diffusivity, melt viscosity, surface tension and the properties of polymer and gas. Thus the new cell growth theory is founded. The new model is applied into a flat part moulding process and the effect trend of melt temperature, pre-filled volume, injection time, cooling time and SCF percentage on the cell growth is studied.Based on the present nucleation and cell growth model, the effect proportion of process parameters on cell morphology is gotten by using of the numerical simulation and Taguchi experiment methods. The process conditions adjustment programme is proposed to avoid the shortcomings of microcellular foam injection molding parts. Thus the relationship model between main process parameters and cell morphology is gotten by multiple regression analysis method. The regression model is used as objective function in the optimization process. The optimization method is simulated annealing. The total process condition design method is used into the flat model and good result is obtianed. Thus the precision of microcellular foam injection molding process parameters design is guaranteed.The process conditions design system model , which is based on the numerical simulation technology, is founded. And then the whole computer aided design software system of microcellular foam injection molding process design system is programed by visual basic language. The software system includes Taguchi experimet design system and process condition design sysetm. In the latter system, the improved nucleation and cell growth models are integrated. With Taguchi experiment design method, multiple regression analysis method and simulated annealing, the accuracy of computer aided design system of process conditions has been ensured.At last the microcellular foam injection moulding process design system is used into the realitical production of complicated injection part. The process parameters are optimised through the process design methods and software system that are presented in this study. The optimized process conditions reduce the part warpage form 1.8mm to 0.3mm. Thus the part quality is improved and satisfied with the part design requirement. All these show the theories and deisgn methods in the study is accurate and effective on the actual production.更多还原